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MEG Beam Line Studies. E5 Z-Branch Collaborative Effort !!!. Topics to be Addressed. Overview Current Component Status Beam spot size Summary / Conclusions Beam Line Commissioning Schedule. Beam Line Overview. Beam Line Objectives
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MEG Beam Line Studies E5 Z-Branch Collaborative Effort !!! MEG-Review July 2004
Topics to be Addressed • Overview • Current Component Status • Beam spot size • Summary / Conclusions • Beam Line Commissioning Schedule MEG-Review July 2004
Beam Line Overview • Beam Line Objectives • Couple ‘Z’-Branch elements in shielding to the detector i.e. COBRA • Stop maximum number of μ+ in thinnest target with minimal background contamination • No Iron allowed in vicinity COBRA→ Solenoid coupling • 28 MeV/c surface μ+ beam with high transmission efficiency→ Rate • Reject beam e+ background e+/μ+~ 10→Wien Filter • Small beam spot size at target in COBRA→ careful optics + collimator system + solenoid • Thin slanted target min. thickness for → 37 mg/cm2CH2 Tg at 22 + degrader system E5 Area MEG-Review July 2004
Beam Line Overview Contd. • Collimator system • Beam Transport Solenoid BTS • Degrader + Collimator system • Target system + He-Bag System • Triplet I • Wien Filter E^B Separator • Triplet II MEG-Review July 2004
Trip. Colli. WIEN Solenoid µ+ µ+ Triplet 2 e+ e+ Filter 1 Recap Previous Main Results P-Spectra: -Kinematic Edge (29.79 MeV/c) Theoretical func. P3.5 folded with Gaussian ΔP/P + Const. Cloud µ+ contribution Integrated Rate 4cm Tg.E @ 1800µA Nµ~1.3·108 µ+/s (2.3·108 µ+/s 6cm Tg.) Integrated Rate After Separator 4cm Tg.E @ 1800µA Nµ~9.4·107 µ+/s (1.7·108 µ+/s 6cm Tg.) Ne/Nµ > 9 Ne~ 8.7·108 e+/s Transmission Factors TSep= (71±5)% TColli= (90±5)% “Z-Branch” Pcent=(28.2±0.1)MeV/c ΔP/P =(7.9±0.6)% FWHM PBeam=(28.2±0.9)MeV/c Consistent with TURTLE & P-Slit settings/Calib. MEG-Review July 2004
Trip. Colli. WIEN Solenoid µ+ µ+ Triplet 2 e+ e+ Filter 1 Previous Main Results contd… Integrated Rate After PSC Solenoid !!! 4cm Tg.E @ 1800µA Nµ~6.1·107 µ+/s (1.1·108 µ+/s 6cm Tg.) Beam Spot: σX ~ 5.3 mm σY~ 6.5 mm Transmission Factor Solenoid TSol= 71 % Integrated Rate 4cm Tg.E @ 1800µA Nµ~8.5·107 µ+/s (1.5·108 µ+/s 6cm Tg.) µ/e Separation 11.8cm 7.2σ !!! With larger Bore i.e. BTS T>71% MEG-Review July 2004
e+ Foils CH2 at focus Solenoid µ+ CH2 Tg Fix Degrader Var. Tg Degrader & Stopping Distribution Measurements Target Thickness vs. NaI Rate Michel Range Curve using NaI: AIR VAC R ~ 870 µ CH2 Degrader Target Target 88% stopped in 400µ CH2 Tg. Measurement Simulation Fix Degrader 600 µ GEANT say 580µ Nearly all Stopped in 400µ • GivesRMean = 1150µ • Equiv GEANT + TRIM • 88% STOP in 400µ Tg !!! MEG-Review July 2004
Component Status • Beam Line Commissioning Started – • E5 Zone totally refurbished, primary installation work – Completed • LHe + LN2 Transfer Lines to zone – Design close to finished ready for ordering PSC PSC shown here Triplet I Separator II Triplet II BTS-Solenoid New Old + New New New Completed Completed MEG-Review July 2004
Current Component Status – Triplet I • Triplet I: FINISHED • - Constructed from QSB Quadrupole magnetsμE4 Shutdown2004 Until May May 2004 May 2004 Planned Insertion Shutdown → Delay due to LEMs Beam planned 5th-6th May → Delay Magnet Group due to LEMs Beam Planned 19th May… Ready but !!! →Crane Problem shielding cannot be removed FINAL Insertion 2nd June May 2004 June 2004 MEG-Review July 2004
Current Component Status – Separators • Old Separator II • - previously used vertical separator • defective most of last Test Beam 2003 • June 2004 Repaired with new power supply • → to be used Commissioning Phase I, • successfullyconditioned to 195 KV • → ONLY available until August 2004 for MEG • New Vertical Separator • approved for MEG • Originally So-called copy of LEMs separator • modified design underway & HV-parts ordered • or delivered • Vmax 200 KV • Dplates 18 cm • Leff 70 cm • Expected End 2004 !!! Vmax 200 KV Dplates 18 cm Leff 70 cm MEG-Review July 2004
Current Component Status – Triplet II New Triplet II:Finished - LEMs magnets shorter version of old Triplet II using 3 QSK quadrupole magnets …better Old Triplet II Presently in storage → will be implemented during Phase I Commissioning 23rd June – Mid August 2004 MEG-Review July 2004
Current Component Status – BTS • Beam Transport Solenoid BTS: • Design Problems SOLVED • Design Parameters submitted Novosibirsk (mid April) detailed design underway • Contract end June • Design, testing + manufacture 9 months (end March 2005) • Waiting for other tenders at present COBRA BTS Full simulations performed with GEANT (from colli. System to target in COBRA) Part simulations done with Graphics TRANSPORT & TURTLE, ANSYS & TRACK → input measured beam phase space from test beam results → all major parameters studied Conclusion: beam spot-size 5mmat targetnot possible without loss of rate !!! Possible consequences for experiment? MEG-Review July 2004
Single Node Trip I Trip II Double Node COBRA ASC Sep Y X BTS BTS continued TRANSPORT Optics ( BTS COBRA optics only schematic here) Axial Field Coupling Centre COBRA → Centre BTS Summed ++ BTS COBRA Summed +- Various Excitations + Coupling Schemes tested SNM, DNM, Reversed Field, Compensation so Final Solution→ Maximum Flexibility MEG-Review July 2004
Current Component Status – BTS cont. • Summary of Main Results (same Polarity solenoids) • No Degrader, No vacuum Window, No He → spot-size ~ 5mm • He Only → spot-size 25 % larger • Full Degrader in BTS all materials → spot-size ~ 15mm • Degrader Intermediate focus inside COBRA → spot-size ~ 10mm • (potential background source) • Split Degrader BTS + intermediate focus → spot-size ~ 13mm • Beam-spot Size • Divergence & Multiple scattering + lever-arm IMPORTANT!!! • He less important • Radial + Axial Focussing • depends on: Beam Divergence & Fringe Field of Solenoids • Radial component & hence focussing Enhanced by opposite polarity fields!!! • BTS reverse polarity wrt Compensation Coils + COBRA • Spot-size reduced 30 %compared with same polarity!!! MEG-Review July 2004
Current Component Status – BTS cont. DNM Reverse Field Soln BTS COBRA BTS P ~ 6 MeV/c P ~ 4 MeV/c COBRA 10 mm Reverse polarity Like polarity Radial Focussing Radial Defocusing MEG-Review July 2004
Transmission Profile (no Target) 12% He loss 3% Decays Degrader No loss Current Component Status – BTS cont. BTS Soln: DNM Reversed Field DNM & SNM Like Polarity allowed by final Specs He 240µ CH2 eq 86% Confirmed in Test Beam 88% µ+stopped in 400µ CH2Tg BTS TRANS 98% BTS-COBRA TRANS = 85% Rstops= Rµ · TRANS· STOP Rµ = 8.5·107 µ+s-1at 1.8 mA 4cm Tg TRANS = 0.85, STOPS = 0.88 (Stop Rate) RStops = 6.4·107 µ+s-1 at 1.8 mA 4cm Tg (want 2.5·107 s-1 for sensitivity) (1.1·108 µ+ s-1 at 1.8 mA 6cm Tg MEG-Review July 2004
Current Component Status – BTS cont. • Beam-spot Size Reduction • Necessary? →10 mm probably OK from TC, DC simulations • Without rate-loss → very Difficult (sub-surface μ+?) • Use Smaller Target→ He Problem (240 μ CH2 Eq.) missed μ+ Stop at downstream end of • COBRA e+ background or annihilation 511 keV s can one distinguish point-of-origin of background? If so maybe OK • Conclusion: use collimators inside BTS to restrict divergence • BTS specifications fixed won’t change Spot-size • Still time to optimize collimator/degrader layout MEG-Review July 2004
Current Component Status – BTS cont. BTS Final Specifications 2800 mm 2630 mm 380 mm 460 mm 300 mm Machine Drawings in preparation at Novosibirsk MEG-Review July 2004
Effect of Beam Spot Size Simulations by: Wataru Ootani & Hajime Nishiguchi MEG-Review July 2004
Beam Spot Size • In the current design of the beam line, it is difficult to make the beam spot size smaller than 10mm(σ) without loss of beam rate. • Although, it is possible to make it smaller by using collimator, further beam tuning, etc., it is useful to look into the effect of large beam spot on detector performance. MEG-Review July 2004
Effect on Timing Counter MEG-Review July 2004
Hit Distribution • TC geometry: • Larger acceptance to cover most of events: 22.5cm<z<125cm, • 28.5cm<r<29.0cm for φ-counter, 29.5cm<r<31.5cm for z-counter • Beam spot size: • σ=0.5, 1.0, 1.5, 2.0cm MEG-Review July 2004
Efficiency • Timing counter acceptance: • 26cm<z<125cm, 0°<φ<360° • Drift chamber materials are not taken into account. ~3% difference MEG-Review July 2004
Michel Positron Hit Rate ~5% difference MEG-Review July 2004
Trigger Rate • TC filtering with e-γ direction match in 1st level trigger • Suppression factor (= Φe/ΔΦe) • Φe: TC total angular acceptance =150° • ΔΦe: angle range corresponding to calorimeter angle resolution ΔΦγ=7° φrange φrange(ΔΦγ=7°) MEG-Review July 2004
Trigger Rate, cont’d Trigger rate (assuming 20Hz at σ=0.5cm) Suppression factor MEG-Review July 2004
Impact Time Spread Correlation bw/ time and z of impact point Impact time spread intrinsic Should be corrected with reconstructed track-length MEG-Review July 2004
Effect on Drift Chamber MEG-Review July 2004
Signal Positron Bending Diameter • Projected bending diameter of signal positron MEG-Review July 2004
Efficiency Loss MEG-Review July 2004
Trigger Rate If used as 2nd-Level Trigger • Change of count rate in possible trigger window ( bending diameter ±1σ,±2σ,±3σ). • this counting rate is raw rate summed over whole DC system and doesn’t contain other trigger requirements from TC and Xenon. MEG-Review July 2004
Spot-size Summary • Effects of larger beam spot size on performances of timing counter and drift chamber were investigated. • No serious effect was found on both detectors for 10mm beam spot size. MEG-Review July 2004
Summary/Conclusions • Main problem with BTS/COBRA coupling solved • BTS Specification submitted to Novosibirsk (mid-April) expected End • March 2005 • Spot-size at Target expected to be larger than Proposal now 10 mm • not thought to be major problem (simulations TC, DC) • Expected Stop-rate RStops = 6.4·107 µ+s-1 at 1.8 mA 4cm Tg • (1.1·108 µ+ s-1 at 1.8 mA 6cm Tg) • From background & sensitivity want (2.5·107μ+s-1 ) • Triplet I & II Finished • Separator II ready for testing (new HV power supply) • New vertical Separator expected end 2004 • Target + He Bag Design next • Beam Line Commissioning Started, initial results reproduced so far!!! • -beam will also be studied MEG-Review July 2004
MEG Beam Commissioning Schedule Part 2 Part 3 Part 1 MEG-Review July 2004
Schedule Beam Line 2002 2003 2004 2005 Triplet I + II Studies Solenoid BTS New Separator Target Beam Line Commissioning Part 1 Part 2 Studies Triplet I + II Solenoid BTS New Separator Target Sep+BTS+COBRA COBRA+Target Platform Beam Line Commissioning Part 1 Pi beam? Part 2 Part 3 Design Manufactoring Assembly Test Prak. Gotta Gotta ? MEG-Review July 2004 Milestone